US20120111263A1 - Method for the determination of impurities in silicon - Google Patents
Method for the determination of impurities in silicon Download PDFInfo
- Publication number
- US20120111263A1 US20120111263A1 US13/289,485 US201113289485A US2012111263A1 US 20120111263 A1 US20120111263 A1 US 20120111263A1 US 201113289485 A US201113289485 A US 201113289485A US 2012111263 A1 US2012111263 A1 US 2012111263A1
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- Prior art keywords
- silicon
- rod
- monocrystalline
- casing
- diluted
- Prior art date
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- Abandoned
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- 229910052710 silicon Inorganic materials 0.000 title claims abstract description 57
- 239000010703 silicon Substances 0.000 title claims abstract description 57
- 238000000034 method Methods 0.000 title claims abstract description 30
- 239000012535 impurity Substances 0.000 title claims abstract description 17
- 238000010790 dilution Methods 0.000 claims abstract description 34
- 239000012895 dilution Substances 0.000 claims abstract description 34
- 229910021420 polycrystalline silicon Inorganic materials 0.000 claims abstract description 27
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 21
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 21
- 239000002019 doping agent Substances 0.000 claims abstract description 21
- 229910021421 monocrystalline silicon Inorganic materials 0.000 claims abstract description 16
- 238000005424 photoluminescence Methods 0.000 claims abstract description 16
- 238000007670 refining Methods 0.000 claims abstract description 7
- 238000005033 Fourier transform infrared spectroscopy Methods 0.000 claims abstract 2
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 52
- 239000013078 crystal Substances 0.000 description 18
- 238000011109 contamination Methods 0.000 description 10
- 229920005591 polysilicon Polymers 0.000 description 9
- 239000000463 material Substances 0.000 description 8
- 239000007858 starting material Substances 0.000 description 6
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 5
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 5
- 229910052796 boron Inorganic materials 0.000 description 5
- 238000005259 measurement Methods 0.000 description 5
- 229910052698 phosphorus Inorganic materials 0.000 description 5
- 239000011574 phosphorus Substances 0.000 description 5
- 238000012545 processing Methods 0.000 description 4
- 238000005204 segregation Methods 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 3
- 238000000151 deposition Methods 0.000 description 3
- 230000008021 deposition Effects 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 239000012495 reaction gas Substances 0.000 description 3
- ZDHXKXAHOVTTAH-UHFFFAOYSA-N trichlorosilane Chemical compound Cl[SiH](Cl)Cl ZDHXKXAHOVTTAH-UHFFFAOYSA-N 0.000 description 3
- 239000005052 trichlorosilane Substances 0.000 description 3
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 2
- BLRPTPMANUNPDV-UHFFFAOYSA-N Silane Chemical compound [SiH4] BLRPTPMANUNPDV-UHFFFAOYSA-N 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 239000000945 filler Substances 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- 238000003908 quality control method Methods 0.000 description 2
- 238000001953 recrystallisation Methods 0.000 description 2
- 239000004065 semiconductor Substances 0.000 description 2
- 239000011856 silicon-based particle Substances 0.000 description 2
- 235000012431 wafers Nutrition 0.000 description 2
- 239000005046 Chlorosilane Substances 0.000 description 1
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 1
- 238000004566 IR spectroscopy Methods 0.000 description 1
- 229910003822 SiHCl3 Inorganic materials 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910052785 arsenic Inorganic materials 0.000 description 1
- RQNWIZPPADIBDY-UHFFFAOYSA-N arsenic atom Chemical compound [As] RQNWIZPPADIBDY-UHFFFAOYSA-N 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 238000005229 chemical vapour deposition Methods 0.000 description 1
- KOPOQZFJUQMUML-UHFFFAOYSA-N chlorosilane Chemical group Cl[SiH3] KOPOQZFJUQMUML-UHFFFAOYSA-N 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 238000004821 distillation Methods 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 238000007667 floating Methods 0.000 description 1
- 239000012634 fragment Substances 0.000 description 1
- 239000008187 granular material Substances 0.000 description 1
- 229910000041 hydrogen chloride Inorganic materials 0.000 description 1
- IXCSERBJSXMMFS-UHFFFAOYSA-N hydrogen chloride Substances Cl.Cl IXCSERBJSXMMFS-UHFFFAOYSA-N 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000004377 microelectronic Methods 0.000 description 1
- 239000012768 molten material Substances 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 238000011002 quantification Methods 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 235000012239 silicon dioxide Nutrition 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
- 238000004857 zone melting Methods 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B13/00—Single-crystal growth by zone-melting; Refining by zone-melting
- C30B13/04—Homogenisation by zone-levelling
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/60—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape characterised by shape
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/02—Silicon
- C01B33/037—Purification
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/02—Elements
- C30B29/06—Silicon
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
- G01N21/3563—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing solids; Preparation of samples therefor
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
- G01N21/64—Fluorescence; Phosphorescence
- G01N21/6489—Photoluminescence of semiconductors
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/84—Systems specially adapted for particular applications
- G01N21/88—Investigating the presence of flaws or contamination
- G01N21/94—Investigating contamination, e.g. dust
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
- G01N21/3563—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing solids; Preparation of samples therefor
- G01N2021/3568—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing solids; Preparation of samples therefor applied to semiconductors, e.g. Silicon
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
- G01N2021/3595—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using FTIR
Definitions
- the invention relates to a method for the determination of impurities in silicon.
- raw silicon is obtained by the reduction of silicon dioxide with carbon in an arc furnace at temperatures of about 2000° C.
- the metallurgical silicon needs to be purified.
- gaseous hydrogen chloride at 300-350° C. in a fluidized bed reactor to form a gas containing silicon, for example trichlorosilane.
- This gas containing highly pure silicon is then used as a starting material for the production of highly pure polycrystalline silicon.
- the polycrystalline silicon often also abbreviated to polysilicon, is conventionally produced by means of the Siemens process.
- thin filament rods of silicon are heated by direct passage of current in a bell-shaped reactor (“Siemens reactor”) and a reaction gas comprising a silicon-containing component and hydrogen is introduced.
- the filament rods are conventionally fitted vertically into electrodes located on the bottom of the reactor, via which the connection to the electricity supply is established. Respective pairs of filament rods are coupled by means of a horizontal bridge (likewise made of silicon) and form a support body for the silicon deposition.
- the typical U-shape of the support bodies, also referred to as thin rods, is produced by the bridge coupling.
- these polysilicon rods are conventionally processed further by means of mechanical processing to form chunks of different size classes, optionally subjected to wet chemical cleaning and finally packaged.
- the polysilicon may, however, also be processed further in the form of rods or rod segments. This applies in particular for use of the polysilicon in FZ methods.
- the polycrystalline silicon thereby produced has the form of granules (granular poly).
- Polycrystalline silicon (abbreviation: polysilicon) is used as a starting material for the production of monocrystalline silicon by means of crucible pulling (Czochralski or CZ method) or by means of zone melting (float zone or FZ method). This monocrystalline silicon is cut into wafers and, after a multiplicity of mechanical, chemical and chemical-mechanical processing operations, is used in the semiconductor industry to fabricate electronic components (chips).
- polycrystalline silicon is required to an increased extent for the production of monocrystalline or polycrystalline silicon by means of pulling or casting methods, this monocrystalline or polycrystalline silicon being used to fabricate solar cells for photovoltaics.
- the polysilicon produced is converted into monocrystalline material for the purpose of quality control.
- the monocrystalline material is tested.
- metal contaminations which are to be regarded as particularly critical for customer processes in the semiconductor industry, are particularly important.
- the silicon is, however, also tested for carbon as well as dopants such as aluminum, boron, phosphorus and arsenic.
- Dopants are analyzed according to SEMI MF 1398 on an FZ single crystal produced from the polycrystalline material (SEMI MF 1723) by means of photoluminescence.
- SEMI MF 1630 low-temperature FTIR (Fourier transform IR spectroscopy) is employed (SEMI MF 1630).
- FTIR SEMI MF 1188, SEMI MF 1391) makes it possible to determine carbon and oxygen concentrations.
- a polycrystalline feed rod is gradually melted with the aid of a radiofrequency coil and the molten material is converted into a single crystal by seeding with a monocrystalline seed crystal and subsequent recrystallization.
- the diameter of the resulting single crystal first increases conically (cone formation) until a desired final diameter is reached (rod formation).
- the single crystal is also mechanically supported in order to relieve the load on the thin seed crystal.
- DE 41 37 521 B4 describes a method for analyzing the concentration of impurities in silicon particles, characterized in that particulate silicon is placed in a silicon vessel, the particulate silicon and the silicon vessel are processed to form monocrystalline silicon in a floating zone and the concentration of impurities, which are present in the monocrystalline silicon, is determined.
- the particulate silicon is intended to be of electronics quality or an equivalent quality.
- the particulate silicon may be polycrystalline or monocrystalline particles or fragments.
- a disadvantage with the method is that there must be sufficient contact between the particles and the silicon vessel, in order to ensure sufficient heat transfer. This entails the risk that the silicon to be analyzed will become contaminated.
- the object is achieved by a method for the determination of impurities in silicon, in which a monocrystalline rod is produced by means of zone refining from silicon to be tested; this monocrystalline rod is introduced, in at least one dilution step, into a casing made of mono- or polycrystalline silicon having defined carbon and dopant concentrations and a diluted monocrystalline rod of silicon is produced from the rod and casing by means of zone refining; wherein the determination of impurities in the silicon to be tested is carried out with the aid of a diluted monocrystalline rod by means of photoluminescence or FTIR or both.
- the silicon to be tested has a carbon content of at least 1 ppma and a dopant content of at least 1 ppba before the at least one dilution step.
- further dilution steps are carried out with a further casing made of mono- or polycrystalline silicon having defined carbon and dopant concentrations and the new monocrystalline rod of silicon respectively obtained after the preceding dilution step, in order to produce a diluted monocrystalline silicon rod.
- dilution steps are carried out until the diluted silicon rod has a carbon content of less than 1 ppma and a dopant content of less than 1 ppba.
- the starting point of the method is processed metallurgical silicon or polycrystalline silicon, which is contaminated with carbon and with dopants.
- the material is contaminated with carbon and/or dopants in such a way that a measurement of the impurities by means of photoluminescence is not initially possible.
- the starting material is preferably in the form of a thin rod, as obtained after deposition on a filament rod in a Siemens reactor.
- a single crystal is grown from this thin rod by means of FZ (float zone) zone refining.
- This monocrystalline rod has a circular cross section and preferably a diameter of from 2 to 35 mm.
- a so-called thin neck is preferably pulled in order to achieve dislocation-free growth and obtain a suitable rod as a filler of the casing for the dilution step.
- the monocrystalline rod grown from the starting material is subsequently introduced into a casing made of monocrystalline or polycrystalline silicon.
- the monocrystalline (or polycrystalline) rod which is contained in the silicon casing, is then converted into a monocrystalline rod by means of FZ.
- a so-called thin neck is preferably pulled in order to achieve dislocation-free growth and obtain a suitable rod as a filler of the casing for the subsequent dilution step.
- the internal diameter of the casing corresponds approximately to the diameter of the monocrystalline rod previously produced.
- the rod diameter is, however, also possible and particularly preferable for the rod diameter to be less than the internal diameter of the casing.
- any mechanical processing of the cylindrical crystal can furthermore be obviated. This is advantageous not least since such mechanical processing could always constitute a cause of additional contamination.
- the silicon casing may be produced from a mono- or polycrystalline rod by boring it out.
- the mono- or polycrystalline material of the casing has a defined level of contamination with carbon and dopants.
- the concentration of impurities in the silicon casing is ideally at a much lower level than the concentration in the silicon to be tested.
- Dilution of the impurities is therefore achieved by the growth of a new rod from the casing and the original rod.
- the concentration of impurities is already at a level which permits determination of the concentration by means of photoluminescence after the first dilution step, no further dilution step is preferably carried out.
- the concentration of impurities is then at a level which permits determination of the concentration by means of photoluminescence when the carbon content is less than 1 ppma and the dopant content is less than 1 ppba.
- Rod-shaped samples of polycrystalline silicon and metallurgical silicon were tested.
- the samples had a diameter of about 5 mm.
- Monocrystalline rods with a diameter of about 12 mm were grown from these samples by means of FZ.
- Undoped polycrystalline silicon casings (diameter about 19 mm) were used as casings.
- the concentrations of the dopants were in the measurable range.
- a measurement wafer was taken from a defined position of the single crystal and was subjected to photoluminescence measurements.
- the concentrations of the original samples could be found therefrom. 1.0 ppma of phosphorus and 6.3 ppma of boron were found.
Abstract
The invention relates to a method for the determination of impurities in silicon, in which a monocrystalline rod is produced by means of zone refining from a silicon to be tested; this monocrystalline rod is introduced, in at least one dilution step, into a casing made of mono- or polycrystalline silicon having defined carbon and dopant concentrations and a diluted monocrystalline rod of silicon is produced from the rod and casing by means of zone refining; wherein the determination of impurities in the silicon to be tested is carried out with the aid of a diluted monocrystalline rod by means of photoluminescence or FTIR or both.
Description
- The invention relates to a method for the determination of impurities in silicon.
- On the industrial scale, raw silicon is obtained by the reduction of silicon dioxide with carbon in an arc furnace at temperatures of about 2000° C.
- So-called metallurgical silicon (Simg, “metallurgical grade”) with a purity of about 98-99% is thereby obtained.
- For applications in photovoltaics and microelectronics, the metallurgical silicon needs to be purified.
- To this end, for example, it is reacted with gaseous hydrogen chloride at 300-350° C. in a fluidized bed reactor to form a gas containing silicon, for example trichlorosilane.
- This is followed by distillation steps, in order to purify the gas containing silicon.
- This gas containing highly pure silicon is then used as a starting material for the production of highly pure polycrystalline silicon.
- The polycrystalline silicon, often also abbreviated to polysilicon, is conventionally produced by means of the Siemens process. In this case, thin filament rods of silicon are heated by direct passage of current in a bell-shaped reactor (“Siemens reactor”) and a reaction gas comprising a silicon-containing component and hydrogen is introduced.
- During the Siemens process, the filament rods are conventionally fitted vertically into electrodes located on the bottom of the reactor, via which the connection to the electricity supply is established. Respective pairs of filament rods are coupled by means of a horizontal bridge (likewise made of silicon) and form a support body for the silicon deposition. The typical U-shape of the support bodies, also referred to as thin rods, is produced by the bridge coupling.
- Highly pure polysilicon is deposited on the heated rods and the bridge, so that the rod diameter increases with time (CVD=chemical vapor deposition).
- After the end of the deposition, these polysilicon rods are conventionally processed further by means of mechanical processing to form chunks of different size classes, optionally subjected to wet chemical cleaning and finally packaged.
- The polysilicon may, however, also be processed further in the form of rods or rod segments. This applies in particular for use of the polysilicon in FZ methods.
- The silicon-containing component of the reaction gas is generally monosilane or a halosilane with the general composition SiHnX4-n, (n=0, 1, 2, 3; X=Cl, Br, I). It is preferably a chlorosilane, particularly preferably trichlorosilane. SiH4 or SiHCl3 (trichlorosilane, TCS) in a mixture with hydrogen is predominantly used.
- Besides this, it is also known to expose small silicon particles directly to such a reaction gas in a fluidized bed reactor. The polycrystalline silicon thereby produced has the form of granules (granular poly).
- Polycrystalline silicon (abbreviation: polysilicon) is used as a starting material for the production of monocrystalline silicon by means of crucible pulling (Czochralski or CZ method) or by means of zone melting (float zone or FZ method). This monocrystalline silicon is cut into wafers and, after a multiplicity of mechanical, chemical and chemical-mechanical processing operations, is used in the semiconductor industry to fabricate electronic components (chips).
- In particular, however, polycrystalline silicon is required to an increased extent for the production of monocrystalline or polycrystalline silicon by means of pulling or casting methods, this monocrystalline or polycrystalline silicon being used to fabricate solar cells for photovoltaics.
- Since the quality requirements for polysilicon are becoming ever higher, quality controls throughout the process chain are indispensable. The material is tested, for example, for contamination with metals or dopants. Distinction is to be made between bulk contamination and surface contamination of the polysilicon chunks or rod segments.
- It is also conventional for the polysilicon produced to be converted into monocrystalline material for the purpose of quality control. In this case, the monocrystalline material is tested. Here again, metal contaminations, which are to be regarded as particularly critical for customer processes in the semiconductor industry, are particularly important. The silicon is, however, also tested for carbon as well as dopants such as aluminum, boron, phosphorus and arsenic.
- Dopants are analyzed according to SEMI MF 1398 on an FZ single crystal produced from the polycrystalline material (SEMI MF 1723) by means of photoluminescence. As an alternative, low-temperature FTIR (Fourier transform IR spectroscopy) is employed (SEMI MF 1630). FTIR (SEMI MF 1188, SEMI MF 1391) makes it possible to determine carbon and oxygen concentrations.
- The fundamentals of the FZ method are described, for example, in DE-3007377 A.
- In the FZ method, a polycrystalline feed rod is gradually melted with the aid of a radiofrequency coil and the molten material is converted into a single crystal by seeding with a monocrystalline seed crystal and subsequent recrystallization. During the recrystallization, the diameter of the resulting single crystal first increases conically (cone formation) until a desired final diameter is reached (rod formation). In the cone formation phase, the single crystal is also mechanically supported in order to relieve the load on the thin seed crystal.
- It has, however, been found that polycrystalline silicon with high extrinsic substance concentrations and highly contaminated material, for example processed metallurgical silicon (“upgraded metallurgical grade”, UMG), which was converted into an FZ single crystal cannot readily be analyzed by means of photoluminescence or FTIR. The contaminations are too high for the range measurable by means of photoluminescence or FTIR. For dopants, concentrations of the order of ppta can be measured by PL (photoluminescence), and for carbon concentrations of the order of ppba can be measured by FTIR.
- DE 41 37 521 B4 describes a method for analyzing the concentration of impurities in silicon particles, characterized in that particulate silicon is placed in a silicon vessel, the particulate silicon and the silicon vessel are processed to form monocrystalline silicon in a floating zone and the concentration of impurities, which are present in the monocrystalline silicon, is determined.
- It is regarded as advantageous in this method that the sample is contaminated minimally by the method. The particulate silicon is intended to be of electronics quality or an equivalent quality. The particulate silicon may be polycrystalline or monocrystalline particles or fragments.
- If the silicon to be tested is already of electronics quality, the problems observed in the prior art with photoluminescence measurements do not arise since the contaminations are at a sufficiently low level. Here, it is paramount that a different shape, namely a rod shape, can be imparted to the particulate silicon by the float zone method in order to be able to carry out such measurements.
- A disadvantage with the method is that there must be sufficient contact between the particles and the silicon vessel, in order to ensure sufficient heat transfer. This entails the risk that the silicon to be analyzed will become contaminated.
- The object of the invention resulted from the described problems.
- The object is achieved by a method for the determination of impurities in silicon, in which a monocrystalline rod is produced by means of zone refining from silicon to be tested; this monocrystalline rod is introduced, in at least one dilution step, into a casing made of mono- or polycrystalline silicon having defined carbon and dopant concentrations and a diluted monocrystalline rod of silicon is produced from the rod and casing by means of zone refining; wherein the determination of impurities in the silicon to be tested is carried out with the aid of a diluted monocrystalline rod by means of photoluminescence or FTIR or both.
- Preferably, the silicon to be tested has a carbon content of at least 1 ppma and a dopant content of at least 1 ppba before the at least one dilution step.
- Preferably, after the at least one dilution step, further dilution steps are carried out with a further casing made of mono- or polycrystalline silicon having defined carbon and dopant concentrations and the new monocrystalline rod of silicon respectively obtained after the preceding dilution step, in order to produce a diluted monocrystalline silicon rod.
- Preferably, further dilution steps are carried out until the diluted silicon rod has a carbon content of less than 1 ppma and a dopant content of less than 1 ppba.
- The starting point of the method is processed metallurgical silicon or polycrystalline silicon, which is contaminated with carbon and with dopants. The material is contaminated with carbon and/or dopants in such a way that a measurement of the impurities by means of photoluminescence is not initially possible.
- The starting material is preferably in the form of a thin rod, as obtained after deposition on a filament rod in a Siemens reactor.
- A single crystal is grown from this thin rod by means of FZ (float zone) zone refining.
- This monocrystalline rod has a circular cross section and preferably a diameter of from 2 to 35 mm.
- Before the final diameter of from 2 to 35 mm is reached during the FZ growth, a so-called thin neck is preferably pulled in order to achieve dislocation-free growth and obtain a suitable rod as a filler of the casing for the dilution step.
- The monocrystalline rod grown from the starting material is subsequently introduced into a casing made of monocrystalline or polycrystalline silicon.
- The monocrystalline (or polycrystalline) rod, which is contained in the silicon casing, is then converted into a monocrystalline rod by means of FZ. Here again, a so-called thin neck is preferably pulled in order to achieve dislocation-free growth and obtain a suitable rod as a filler of the casing for the subsequent dilution step.
- Preferably, the internal diameter of the casing corresponds approximately to the diameter of the monocrystalline rod previously produced.
- It is, however, also possible and particularly preferable for the rod diameter to be less than the internal diameter of the casing.
- Specifically, it has been found that dislocation-free growth is possible even if there is a gap between the internal wall of the casing and the outer surface of the monocrystalline rod.
- Preferably, there is no contact between the casing and the cylindrical crystal. The fact that such an arrangement provides a defect-free single crystal, which may also be used as the starting material for further dilution steps, is surprising.
- If there is no contact between the casing and the cylindrical crystal, any mechanical processing of the cylindrical crystal can furthermore be obviated. This is advantageous not least since such mechanical processing could always constitute a cause of additional contamination.
- The silicon casing may be produced from a mono- or polycrystalline rod by boring it out.
- By producing a new monocrystalline rod from the original monocrystalline (or polycrystalline) rod and the silicon casing, it is possible to dilute the concentration of extrinsic substances in the silicon.
- The mono- or polycrystalline material of the casing has a defined level of contamination with carbon and dopants. The concentration of impurities in the silicon casing is ideally at a much lower level than the concentration in the silicon to be tested.
- Dilution of the impurities is therefore achieved by the growth of a new rod from the casing and the original rod.
- It is also preferable to carry out such a dilution step several times.
- In the case of highly contaminated starting material, such repeated dilution operations are absolutely necessary in order to reach the ranges which can be measured by means of photoluminescence.
- This can be done by introducing the monocrystalline rod obtained after the first dilution step again into a silicon casing and subjecting the rod/casing to an FZ process once more.
- Further dilution of the concentration of impurities is achieved by each additional dilution step.
- If the concentration of impurities is already at a level which permits determination of the concentration by means of photoluminescence after the first dilution step, no further dilution step is preferably carried out.
- The concentration of impurities is then at a level which permits determination of the concentration by means of photoluminescence when the carbon content is less than 1 ppma and the dopant content is less than 1 ppba.
- When determining the concentrations by means of photoluminescence, the dilution must of course be taken into account. Yet since the degree of contamination of the material of the silicon casing is known, i.e. it lies in the range which can be measured by means of photoluminescence, it is no problem for the person skilled in the art to determine the exact concentration of the contamination in the silicon to be tested by means of the concentration of the impurities in the single crystal produced from (rod/casing), or after n dilution steps in the single crystal produced from (rod/n*casing).
- In the case of high crystal growth rates of more than 10 mm/min, which is preferred, segregation may be neglected to first approximation since high segregation coefficients occur. The cylindrical single crystal used, which preferably has a crystal diameter of 2-35 mm, is preferably produced with such a high pulling rate and low effective melt height. For boron and phosphorus, virtually no segregation effects then take place, which makes the method less complicated, all the more so since segregation effects have always had to be taken into account in the prior art (SEMI MF 1723-1104).
- It has been found that the method permits quantification of the doping elements by the photoluminescence method even with unlimitedly high dopant concentrations.
- Rod-shaped samples of polycrystalline silicon and metallurgical silicon were tested.
- The samples had a diameter of about 5 mm.
- Monocrystalline rods with a diameter of about 12 mm were grown from these samples by means of FZ.
- Undoped polycrystalline silicon casings (diameter about 19 mm) were used as casings.
- 4 dilution steps were carried out.
- After the first three dilution steps, the concentrations of boron and phosphorus were not in the measurable range.
- After the fourth dilution step, the concentrations of the dopants were in the measurable range.
- For this purpose, a measurement wafer was taken from a defined position of the single crystal and was subjected to photoluminescence measurements.
- 79 ppta of phosphorus and 479 ppta of boron were found.
- The concentrations of the original samples could be found therefrom. 1.0 ppma of phosphorus and 6.3 ppma of boron were found.
- With respect to carbon, its concentration already lay in the measurable range after the third dilution. It was 87 ppba.
- For the original sample, 833 ppma of carbon were calculated.
Claims (6)
1. A method for determining impurities in silicon, comprising:
zone refining the silicon to produce a monocrystalline rod;
conducting at least one dilution step to introduce the monocrystalline rod into a casing comprising mono- or polycrystalline silicon having defined carbon and dopant concentrations;
zone refining the monocrystalline rod and the casing to produce a diluted monocrystalline rod of silicon; and
conducting at least one of photoluminescence and FTIR on the diluted monocrystalline rod of silicon to determine impurities in the silicon.
2. The method as claimed in claim 1 , wherein the silicon to be tested has a carbon content of at least 1 ppma and a dopant content of at least 1 ppba before the at least one dilution step.
3. The method as claimed in claim 2 , wherein after the at least one dilution step, further dilution steps are carried out with a further casing comprising mono- or polycrystalline silicon having defined carbon and dopant concentrations and a new monocrystalline rod of silicon respectively obtained after the preceding dilution step, in order to produce a diluted monocrystalline silicon rod.
4. The method as claimed in claim 3 , wherein dilution steps are carried out until the diluted silicon rod has a carbon content of less than 1 ppma and a dopant content of less than 1 ppba.
5. The method as claimed in claim 1 , wherein after the at least one dilution step, further dilution steps are carried out with a further casing comprising mono- or polycrystalline silicon having defined carbon and dopant concentrations and a new monocrystalline rod of silicon respectively obtained after the preceding dilution step, in order to produce a diluted monocrystalline silicon rod.
6. The method as claimed in claim 5 , wherein dilution steps are carried out until the diluted silicon rod has a carbon content of less than 1 ppma and a dopant content of less than 1 ppba.
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DE102010043702A DE102010043702A1 (en) | 2010-11-10 | 2010-11-10 | Method for the determination of impurities in silicon |
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EP (1) | EP2453042B1 (en) |
JP (1) | JP5259805B2 (en) |
KR (1) | KR101359076B1 (en) |
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Cited By (3)
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US20130260540A1 (en) * | 2012-02-23 | 2013-10-03 | Fuji Electric Co., Ltd | Method of manufacturing semiconductor device |
US20160068949A1 (en) * | 2013-04-22 | 2016-03-10 | Wacker Chemie Ag | Process for the preparation of polycrystalline silicon |
CN111801782A (en) * | 2018-03-16 | 2020-10-20 | 信越半导体株式会社 | Carbon concentration evaluation method |
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JP6300104B2 (en) * | 2014-12-02 | 2018-03-28 | 信越半導体株式会社 | Method for measuring carbon concentration in silicon crystal, method for measuring carbon-related levels in silicon crystal |
CN105092511A (en) * | 2015-08-12 | 2015-11-25 | 南京秀科仪器有限公司 | Method for detecting content of substitutional carbon and interstitial oxygen in monocrystalline silicon |
JP6472768B2 (en) * | 2016-04-08 | 2019-02-20 | 信越化学工業株式会社 | Determination of impurities in silicon crystal by photoluminescence method and selection method of polycrystalline silicon |
JP6693485B2 (en) * | 2017-08-18 | 2020-05-13 | 信越半導体株式会社 | Carbon concentration measurement method |
US20220381761A1 (en) * | 2020-07-21 | 2022-12-01 | Wacker Chemie Ag | Method for determining trace metals in silicon |
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- 2011-10-27 CA CA2756474A patent/CA2756474C/en not_active Expired - Fee Related
- 2011-11-04 US US13/289,485 patent/US20120111263A1/en not_active Abandoned
- 2011-11-08 KR KR1020110115726A patent/KR101359076B1/en not_active IP Right Cessation
- 2011-11-08 EP EP11188214A patent/EP2453042B1/en not_active Not-in-force
- 2011-11-09 JP JP2011245758A patent/JP5259805B2/en not_active Expired - Fee Related
- 2011-11-09 CN CN201110353075.4A patent/CN102565014B/en not_active Expired - Fee Related
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JP5259805B2 (en) | 2013-08-07 |
JP2012102009A (en) | 2012-05-31 |
CA2756474C (en) | 2013-07-02 |
CN102565014B (en) | 2015-04-08 |
EP2453042B1 (en) | 2013-03-13 |
CA2756474A1 (en) | 2012-05-10 |
KR20120050383A (en) | 2012-05-18 |
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CN102565014A (en) | 2012-07-11 |
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